Factual error: When speaking to a member of the the Royal Family in Siam (modern day Thailand), one have to speak "rachasap" or Royal Thai. The movie depicts characters speaking colloquial Thai to the King.
Factual error: As was the case in Buster Keaton's "The General" film, the General locomotive portrayed in the film more closely resembles the actual locomotive's 1893 appearance rather than its wartime appearance. As built, the General had three domes, an ankle bar on each side running the length of the engine, as well as the Western and Atlantic Railroad's then trademark strap-iron cowcatchers with horizontal slats. The engine was rebuilt in the 1870s, with the bars and third dome removed, and cowcatcher changed to the more conventional design seen in the film. The Radley Hunter Balloon stack the engine had was replaced with a diamond shaped one at this time, as the engine was converted to coal. The engine received a stack more closely resembling its original one in 1893.
Factual error: The Welsh Guards parading at the start of the film weren't formed until 1915. The film is set in 1872.